This invention relates, in general, to completing a well that traverses a hydrocarbon bearing subterranean formation and, in particular, to a system and method for reducing the pressure drop in the fluids produced through a production tubing by expanding the flow area of the production tubing downhole.
Without limiting the scope of the present invention, its background will be described with reference to producing fluid from a subterranean formation, as an example.
After drilling each of the sections of a subterranean wellbore, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation. Conventionally, each section of the casing string is cemented within the wellbore before the next section of the wellbore is drilled. Accordingly, each subsequent section of the wellbore must have a diameter that is less than the previous section.
For example, a first section of the wellbore may receive a conductor casing string having a 20-inch diameter. The next several sections of the wellbore may receive intermediate casing strings having 16-inch, 13xe2x85x9c-inch and 9⅝-inch diameters, respectively. The final sections of the wellbore may received production casing strings having 7-inch and 4xc2xd-inch diameters, respectively. Each of the casing strings may be hung from a casing head near the surface. Alternatively, some of the casing strings may be in the form of liner strings that extend from near the setting depth of previous section of casing. In this case, the liner string will be suspended from the previous section of casing on a liner hanger.
Once this well construction process is finished, the completion process may begin. The completion process may include numerous steps such as creating hydraulic openings or perforations through the production casing string, the cement and a short distance into the desired formation or formations so that production fluids may enter the interior of the wellbore, formation stimulation to enhance production, gravel packing to prevent sand production and the like. The completion process also includes installing a production tubing string within the well that extends from the surface to the production interval or intervals. Unlike the casing strings that form a part of the wellbore itself, the production tubing string is used to produce the well by providing the conduit for formation fluids to travel from the formation depth to the surface.
The diameter of the production tubing that is installed within a well is determined based upon a number of factors. For example, the maximum diameter of the production tubing is limited by the various restrictions within the well including the production casing and any tools within the production casing such as landing nipples. In addition, the production tubing is sized based upon the reservoir pressure, composition of the formation fluids and the expected production rate from the formation. For example, if the production tubing selected for a well is too large, slugging may occur during production in which case a workover may be required to install smaller production tubing or an artificial lift system. On the other hand, if the production tubing selected for a well is too small, the pressure drop in the formation fluids traveling through the production tubing is unnecessarily large and the rate of production from the formation is unnecessarily constrained, in which case, a workover may be required to install larger production tubing.
A need has therefore arisen for a system and method for completing a well that traverses a subterranean formation that minimize the likelihood of installing a production tubing string that is not properly sized for the production from the traversed formation. A need has also arisen for such a system and method that are capable of reducing the pressure drop in the fluids produced through the production tubing when the formation is capable of producing at a higher rate. Further, a need has arisen for such a system and method that do not require a workover to optimize the size of the production tubing.
The present invention disclosed herein comprises a system and method for completing a well that traverses a subterranean formation that minimize the likelihood of installing a production tubing string that is not properly sized for the production from the traversed formation. The system and method of the present invention are capable of reducing the pressure drop in the fluids produced through the production tubing when the formation is capable of producing at a higher rate. Further, the system and method of the present invention do not require a workover to optimize the size of the production tubing.
The well completion system of the present invention comprises a production tubing that is positioned within a well casing that lines the wellbore and an expander member positioned within the production tubing that travels longitudinally within the production tubing to expand the production tubing downhole, thereby reducing the pressure drop in fluids produced through the production tubing. The expansion process may proceed from an uphole location to a downhole location or from a downhole location to an uphole location. The force required to expand the production tubing may be generated by pressurizing at least a portion of the production tubing to urge the expander member to travel longitudinally within the production tubing. This fluid pressure may be delivered directly into the production tubing or may be introduced through a coiled tubing that may be coupled to the expander member. Additionally or alternatively, when coiled tubing is used, the coiled tubing may be placed in tension to mechanically urge the expander member to travel longitudinally within the production tubing.
Broadly stated, one method of the present invention comprises the steps of lining the wellbore with a well casing, disposing the production tubing within the well casing and expanding the production tubing downhole, thereby reducing the pressure drop in fluids produced through the production tubing. The expansion step may be independent of or as a result of first testing the productive capability of the formation traversed by the wellbore to determine whether production from the formation is constrained by the production tubing.
Another method of the present invention comprises the steps of lining a first section of the wellbore with a first well casing having an inner diameter, lining a second section of the wellbore with a second well casing having an inner diameter that is smaller than the inner diameter of the first well casing, disposing the production tubing within the first and the second well casings and expanding the production tubing downhole that is disposed within the first well casing.
Yet another method of the present invention comprises the steps of lining at least a main wellbore portion of a multilateral well with a well casing, extending first and second branch wellbores from the main wellbore, the second branch wellbore being farther downhole than the first branch wellbore, disposing a main section of production tubing within the well casing in the main wellbore, a first branch section of production tubing within the first branch wellbore and a second branch section of production tubing within the second branch wellbore and expanding the production tubing downhole that is uphole of the first branch wellbore. In this method, it may be desirable to expand the flow area of the production tubing that is uphole of the first branch wellbore to substantially match the flow area of the first branch section of production tubing and the flow area of the second branch section of production tubing.